Hydrogen and oxygen supplemental firing for combined cycle facility

ABSTRACT

A combined-cycle power plant comprises a gas turbine engine for generating exhaust gas, an electric generator driven by the gas turbine engine, a steam generator receiving the exhaust gas to heat water and generate steam, and a duct burner system configured to heat exhaust gas in the steam generator before generating the steam and that comprises a source of hydrogen fuel, a fuel distribution manifold to distribute the hydrogen fuel in a duct of the steam generator, and an igniter to initiate combustion of the hydrogen fuel in the exhaust gas. A method for heating exhaust gas in a steam generator for a combined-cycle power plant comprises directing combustion gas of a gas turbine engine into a duct, introducing hydrogen fuel into the duct, combusting the hydrogen fuel and the combustion gas to generate heated gas, and heating water in the duct with the heated gas to generate steam.

TECHNICAL FIELD

This document pertains generally, but not by way of limitation, tocombined-cycle power plants, such as those including gas turbineengines. More specifically, but not by way of limitation, the presentapplication relates to supplemental firing systems for combined-cyclepower plants, such as those that can be used in heat recovery steamgenerators.

BACKGROUND

In a gas turbine combined-cycle (GTCC) power plant, a gas turbine enginecan be operated to directly generate electricity with a generator usingshaft power. Hot exhaust gas of the gas turbine engine can additionallybe used to generate steam within a heat recovery steam generator (HRSG)that can be used to rotate a steam turbine shaft to further produceelectricity.

Output of the HRSG can be increased by increasing the temperature of theexhaust gas, such as by use of a supplemental firing system. In suchsystems, a natural gas fuel can be directed into the duct of the HRSGand ignited via a duct burner to increase the energy and temperature ofthe exhaust gas, thereby increasing the capability of producing steam inthe HRSG.

Examples of combined-cycle power plants using supplemental firingsystems or duct burners are described in U.S. Pat. No. 6,810,675 toLiebig; U.S. Pat. No. 6,606,848 to Rollins III; and Pub. No. US2017/0350279 to Kobayashi et al.

OVERVIEW

Problems to be solved in operating combined-cycle power plants includethe emission of carbon dioxide (CO₂) due to burning of fossil fuels suchas natural gas, which is the most widely used fossil fuel for powergeneration in the United States. The power industry is attempting tomove towards reduced-carbon or carbon-free electricity in response tovarious state icier prompting the drawing down of carbon-based poweralong with the additional eventual transition to 100% renewable energy.However, the present inventors have recognized, among other things, thatcombined-cycle power plants utilize fossil fuels in multiple, disparateplaces within a gas turbine combined-cycle power plant. As such, simplytransitioning a gas turbine engine of a combined-cycle power plant overto burning cleaner fuel will not achieve the lowest emissions possible.

The present subject matter can provide solutions to this problem andother problems, such as by providing methods and systems for providingcarbon-free fuel to a combined-cycle power plant. One portion of thecombined-cycle facility that uses fuel, in addition to the gas turbine(GT), to support the production of electricity is the duct burner thatis located within the HRSG. The duct burner inside of the HRSG providessupplemental heat input to the thermal cycle to provide the capabilityto increase steam production that can be converted to electrical energyvia a steam turbine generator (STG). The duct burner typically usesnatural gas as the fuel.

The present inventors have recognized that duct burners have the abilityto burn a wide range of fuels. One source of carbon-free electricity isvia the use of hydrogen. One such power generation facility that canconvert hydrogen to electricity is a combined-cycle power plant having aduct burner with a fuel source that is at least partially hydrogen.Regardless of the percentage of hydrogen burned, it will produce lowerCO₂ emissions than that of combusting 100% natural gas. Furthermore, thepresent disclosure can use a source of pressurized hydrogen fuel, suchas an electrolyser, at the location of the GTCC power plant.Furthermore, a source of pressurized oxygen, such as the electrolyser,can additionally be located at the GTCC power plant to provide anoxidant to the combustion process. The amount of hydrogen and oxygen canbe controlled or modulated, such as by using a burner management system,to control the supplemental firing combustion process independent of theoperation of the GT, thereby allowing tailored steam production in theHRSG.

In an example, a duct burner system for a combined-cycle power plantcomprising a gas turbine engine configured to generate exhaust gas and asteam generator configured to receive the exhaust gas from the gasturbine to heat water and generate steam, the duct burner system cancomprise a source of hydrogen fuel and a fuel distribution manifoldlocated in the steam generator to distribute the hydrogen fuel across alength of a duct of the steam generator.

In another example, a method for heating exhaust gas in a heat recoverysteam generator for use in a combined-cycle power plant can comprisedirecting combustion gas of a gas turbine engine into a duct,introducing hydrogen fuel into the duct, combusting the hydrogen fueland the combustion gas in the duct to generate heated gas, and heatingwater pipes in the duct with the heated gas to generate steam.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine combined-cycle power plantincluding a supplemental firing unit including sources of hydrogen fueland oxygen.

FIG. 2 is a perspective view of a distribution system including separatemanifolds for introducing hydrogen fuel and oxygen into a duct of a HRSGof the gas turbine combined-cycle power plant of FIG. 1.

FIG. 3 is a schematic cross-sectional view of a hydrogen manifoldincorporating a nozzle.

FIG. 4 is a schematic block diagram of a burner management system foruse in the gas turbine combined-cycle power plant of FIG. 1.

FIG. 5 is a schematic line diagram illustrating methods of generatingand combusting hydrogen fuel and oxygen in a duct burner of acombined-cycle power generation system.

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of combined-cycle power plant 10comprising gas turbine 12, heat recovery steam generator (HRSG) 14,steam turbine 16, supplemental firing system 18, and plant controller20. Gas turbine 12 can be configured to provide input to electricalgenerator 22 and steam turbine can be configured to provide input toelectrical generator 24. Controller 20 can comprise a DistributedControl Systems (DCS) device. HRSG 14 can be operatively coupled tosteam turbine 16. Gas turbine 12 can include compressor 26, combustor 28and turbine 30. Steam turbine 16 can include multiple stages, such ashigh pressure turbine 32 and intermediate/low pressure turbines 34A and34B. Steam turbine 16 can additionally be coupled to condenser 36.Supplemental firing system 18 can comprise duct burner system 38, gasgenerator 40, storage tanks 42A and 42B, control devices 44A and 44B,valves 46A and 46B, expansion device 48 and an optional mixer 50.

Gas turbine 12 can be configured to operate by compressing air incompressor 26, mixing the compressed air with fuel in combustor 28 togenerate high energy gases via burning of the fuel, and then expandingthe high energy gases in turbine 30 to produce rotational shaft power.Rotation of turbine 30 can rotate a shaft to propagate rotation ofcompressor 26 and compression of air therein to maintain the combustionprocess. That same rotational shaft power can be used to turn agenerator shaft to provide input to electric generator 22. Thus,combustion of fuel in combustor 28 is converted to electricity atelectric generator 22.

Gas expanded by turbine 30 can be passed into HRSG 14 to, for example,generate steam for operation of steam turbine 16. HRSG 14 can includeduct burner system 38, as well as other components such as asuperheater, an evaporator, an economizer and a selective catalyticreduction (SCR) system, which are not shown in FIG. 1 for simplicity.Exhaust gas E from turbine 30 can pass by various heat transfercomponents, of HRSG 14 to produce steam and ultimately cause rotation ofturbines 32, 34A and 34B to rotate a steam turbine shaft that providesinput to electrical generator 24. Condenser 36 can collect steam fromsteam turbine 16 and return water condensed therein to HRSG 14 topropagate the steam generation process. Steam turbine 16 and condenser36 can operate in a conventional manner. Thus, generation of heat fromexhaust gas of gas turbine 12 can be converted to electricity atelectric generator 24. Electricity generated by electrical generators 22and 24 can be delivered to end users such as by coupling to adistributed grid network.

In order to increase the output capacity of HRSG 14, e g., the abilityto turn water into steam, the temperature of exhaust gas E of gasturbine 12 can be increased using duct burner system 38. Duct burnersystem 38 can introduce a fuel into duct 52 of HRSG 14 before (e.g.,upstream of) water piping of high pressure and low pressure steamcircuits 54A and 54B. The fuel can mix with the exhaust gas. Duct burnersystem 38 can include one or more ignitors (e.g., ignitors 68A-68C ofFIG. 2) to cause the fuel to burn to increase the temperature of exhaustgas E.

In the present disclosure, duct burner system 38 can utilize hydrogenwith oxygen as an augmenting oxidant to combust and provide supplementalheat to the overall thermal cycle. The oxygen and hydrogen ratio can beindependent from the operating profile of gas turbine 12. As such, ductburner system 38 can provide an expanded operating profile, improvedduct burner flame stability, improved overall thermal efficiency, loweremissions, and enhanced load following capabilities to combined-cyclepower plant 10. The gas products for the supplemental firing, e.g., H₂and O₂, can be produced by electrolyser 40 or can be provided fromindependent sources. In an example, electrolyser 40 can provide H₂ andoxygen can be utilized from ambient air. In such configurations, ambientair provides nitrogen to the combustion process, which can result in theproduction of unwanted emissions. Such emissions can be remedied withthe use of selective catalytic reduction (SCR) systems. In theillustrated embodiment, electrolyser 40 can provide both H₂ and O₂.

Electrolyser 40 generates H₂ and O₂ gas using an electric current. Forexample, water (H₂O) can be decomposed into oxygen (O₂) and hydrogen(H₂). The resulting constituents of the electrolysis process, e.g., O₂and H₂, can be stored in tanks 42A and 42B, respectively. The O₂ and H₂,can be pressurized within tanks 42A and 42B. The pressurization canoccur as a result of the electrolysis process or can be provided byadditional means, such as one or more compressors or pumps.

Each of tanks 42A and 42B can provide a gas such as H₂ or O₂ to ductburner system 38. Flow of the gas can be controlled by control devices44A and 44B in conjunction with modulating valves 46A and 46B.Furthermore, tanks 42A and 42B can be provided with shut-off valves 56Aand 56B. Shut-off valves 56A and 56B can comprise on/off valves thatpermit or obstruct flow of gas from tanks 42A and 42B, respectively.Valves 46A and 46B can comprise modulating valves that can be moved intoa plurality of positions between on and off to allow different amountsof gas to flow therethrough, respectively. Modulating valves 46A and 46Band shut-off valves 56A and 56B can be connected to plant controller 20.

Duct burner system 38 can be configured to combust the combustionconstituents (H₂ and O₂) added to exhaust gas E provided to duct 52 fromgas generator 40 and/or tanks 42A and 42B. As such, in the configurationof FIG. 1, an augmenting oxidant, oxygen (O₂), can be introduced intoduct 52 to support the burning of a fuel, hydrogen (H₂), also introducedinto duct 52.

Fuel and oxidant distribution and flame stability can be supported overa wide range of operating conditions, such as by modulation of valves46A and 46B through BMS 44A and 44B, respectively. Operation of astandard duct burner using natural gas is limited by parameters of thegas turbine exhaust, such as exhaust gas temperature, oxygen level, andflow rate. With supplemental firing system 18 of the present disclosure,a separate supply of O₂ can enable combustion of H₂ in duct 52 withoperation over a wider range of gas turbine exhaust parameters, at leastsomewhat decoupled from the exhaust and operation parameters of gasturbine 12.

The flow of H₂ from tank 42B via valve 46B to duct burner 38 can becontrolled by a hydrogen flow controller incorporated into BMS 44B andin communication with plant controller 20. BMS 44B can modulate thehydrogen flow rate based on sensor signals from GT load sensor 58A, andGT exhaust flow rate sensor 58B, GT exhaust temperature sensors 58C and58D upstream and downstream of duct burner 38, HRSG steam temperaturesensor 58E, oxygen level sensor 58F, as well as the desired total poweroutput of GTCC power plant 10 including the energy input fromhydrogen-fueled duct burner 38. For example, because combustion of H₂/O₂is faster and hotter than natural gas, the amount of H₂/O₂ to becombusted can be based upon the exhaust flow rate as well as HRSG steamtemperature limitations.

The flow of O₂ from tank 42A via valve 46A to duct burner 38 can becontrolled by an oxygen flow controller incorporated into BMS 44A and incommunication with plant controller 20. BMS 44A can control the oxygenflow rate based on the supplemental firing load of the hydrogen and alsothe flow rate and oxygen content of the incoming GT exhaust E to ductburner 38 as well as the exhaust gas temperature both upstream anddownstream of duct burner 38. A target combined oxygen content (from theexhaust gas and external supply) of about 10% to about 20% excess oxygenis expected to provide complete combustion. Oxygen sensors can beprovided in duct 52 to sense the amount of oxygen in exhaust gas Eupstream of duct burner system 38.

The hydrogen and oxygen can be supplied from tanks 42A and 42B viaseparate pipes all the way to the inside of duct 52 of HRSG 14, toprevent flame flashback in the supply pipes, as described with referenceto FIG. 2 for example. Alternatively, the oxygen and hydrogen can bepre-mixed locally, such as within mixer 50, and the mixture can beinjected into the exhaust stream immediately prior to ignition.

The configuration of FIG. 1, as well as other hydrogen-combusting ductburners, can be enhanced with other optional devices and configurationsthat can add value and efficiency to the combustion process to, amongother things reduce emissions. First, fuel pre-heat can increase flamestability, reduce CO, and allow increased flame management to improveNOx control. Because Hydrogen (above 200° K) has a negativeJoule-Thomson coefficient, expansion device 48 can be installed afterboth hydrogen Burner Management System (BMS) 44B and hydrogen flowcontroller (e.g. valve 46B) to provide fuel pre-heat. Expansion device48 can comprise any throttling device design that can provide fuelpre-heat to help reduce CO, and enhance flame stability and NOx control.Because the operating temperature of the hydrogen will always be above200° K, the joule-Thompson coefficient will always remain negative. Thepipe diameter of post-expansion (D2) versus pre-expansion (D1) can alsobe dictated by cycle design specifics but it is always expected that D2will be greater than D1, to accommodate (and potentially maximize) theexpansion. Alternatively, or in addition to, expansion device 48,nozzles can be installed on the duct burner lines, and utilized tofurther expand the hydrogen beyond what the upstream expansion device 48achieves, to obtain further fuel pre-heat, as is illustrated in FIG. 2.Use of nozzles on the duct burner lines can allow for a reduction of thepost-expansion pipe diameter (D2) at the upstream expansion device,which may reduce material cost and complexity. In other examples, fuelheating devices, such as electric heaters or heat exchangers incommunication with other portions of GTCC power plant 10 can be used.

The separately controlled and consistent flows of hydrogen and oxygencan help ensure optimal combustion conditions to maintain flamestability and minimize CO and NO emissions over a wide range of GToperating conditions. The optional components (throttling device, ductburner nozzles) further enhance the operation of the system.

FIG. 2 is a perspective view of distribution system 60 for duct burnersystem 38 including separate manifolds 62A and 62B for introducingoxygen and hydrogen fuel into duct 52 of HRSG 14 of gas turbinecombined-cycle power plant 10 of FIG. 1. Manifolds 62A and 62B canprovide an alternative to mixer 50. As mentioned, mixer 50 can be usedfor premixing oxygen and hydrogen before ignition, which is one way todesign a burner (“premixed flame”). In such a configuration, a singlemanifold can be used to introduce the mixture of oxygen and hydrogeninto duct 52. Alternatively, manifolds 62A and 62B can be used to keepoxygen and hydrogen separate until just before ignition. (so called“diffusion flame”). Duct burner system 38 can be configured either way.

Flow of gas into manifolds 62A and 62B can be controlled by modulatingvalves 46A and 46B, which are operated by control devices 44A and 44B,respectively, in coordination with controller 20. Motive pressure to theoxygen and hydrogen introduced into manifolds 46A and 46B can beprovided by compressors or pumps, electrolyser 40, or by pressurizationof tanks 42A and 42B.

Manifolds 62A and 62B can be configured as elongate tubular elementsthat can extend partially or fully across duct 52, e.g., into the planeof FIG. 1. Multiple longitudinal levels of manifolds 62A and 62B can bevertically provided within duct 52 to distribute the oxygen and hydrogenacross the height of duct 52. Manifolds 62A and 62B can be provided withorifices 64A and 64B, respectively, to permit gas to flow out of theelongate tubular elements. Orifices 64A and 64B can be provided ondownstream or trailing sides of manifolds 62A and 62B, respectively.Ignition system 66 can be provided downstream of manifolds 62A and 62Bto provide one or more sparks or other flame-instigators using ignitors68A, 68B and 68C. Excitor 70 can be coupled to controller 20 to provideenergy to ignitors 68A 68C, such as heat or electricity.

In the illustrated example, the diameter of manifold 62A is shown to begreater than the diameter of manifold 62B. However, the absolute andrelative diameters, or cross-sectional areas for other shapes, formanifolds 62A and 62B, as well as the sizes of orifices 64A and 64B, canbe determined based on the expected operating range of temperature andvolume of exhaust gas E as well as Hydrogen and Oxygen. Orifices 64A and64B can comprise simple through-bores in manifolds 62A and 62B. However,in other examples, orifices 64A and 649 can be configured as or equippedwith nozzles, as is shown in FIG. 3.

FIG. 3 is a schematic cross-sectional view of manifold 72 comprisingtubular body 74, nozzle 76 and deflector 78. Deflector 78 can becontoured to form pocket 80 in which tubular body 74 can be fully orpartially disposed. Deflector 78 can extend fully or partially acrossthe width of duct 52 a length sufficient to shield the width of manifold72.

Manifold 72 can comprise elongate tubular body 74 having a lengthconfigured to span, or at least partially span, the width of duct 52.Manifold 72 can have a partially circular cross-sectional profile, butcan have other shapes. Nozzle 76 can project from tubular body 74, suchas in a radial direction from the center of manifold 72. Manifold 72 canbe positioned within duct 52 such that nozzle 76 projects in adownstream direction, e.g., in a flow direction of exhaust gas E. Nozzle76 can be configured as a narrowing passage, e.g., a converging nozzle,to throttle the exit of the H₂ gas from manifold 72 and thereby providepre-heating to the H₂ gas. However, nozzle 76 can have otherconfigurations, such as converging--diverging. Nozzle 76 can be analternative to expansion device 48 or can be provided in combinationwith expansion device 48 to provide two-stage heating.

Baffle 78 can be provided to slow down or diffuse the flow of exhaustgas E around manifold 72. Baffle 78 can be provided with perforations toallow exhaust gas E to pass through baffle 78. As such, exhaust gas Epassing through and around baffle 78 can be slowed to a velocity moresuited for receiving the H₂ gas from manifold 72 and sustaining thecombustion process, e.g., promoting flame stability.

FIG. 4 is a schematic block diagram of control device 449 comprising aburner management system for duct burner system 38. Control device 44Bof FIG. 4 can be, for example, a computer that is installed in a controlroom for combined-cycle power plant 10, and has a function to controlvalves 46B and 56B. Control device 44B of FIG. 1 can be, for example, acomputer that is installed in a control room for combined-cycle powerplant 10, and has a function to control valves 46A and 56A. FIG. 4 isdescribed with reference to control device 44B, though control device44A can be configured similarly. Controller 20 (FIG. 1) can be incommunication with control devices 44A and 44B and can be configured tocontrol and coordinate operation of gas turbine 12, HRSG 14, and ductburner system 38. Control device 44B can comprise CPU 82, HDD 84, RAM86, ROM (for example, EPROM) 88, and I/O port 90.

Input unit 92, recording medium 94, output unit 96, network 98, can beconnected to I/O port 90 as appropriate, as well as a section of GTCCpower plant 10 to be commanded. The sections to be commanded can includemodulation valve 469 and shut-off valve 569. Operation of duct burnersystem 38, including ignitors 68A-68C and excitor 70, can be controlledby controller 20, which can additionally control other aspects of GTCCpower plant 10 such as fuel flow to gas turbine 12, inlet guide vanes(not depicted), operation of generators 22 and 24, steam turbine 16, gasgenerator 40 and others. As such, operation of GTCC power plant 10including supplemental firing system 18 can be controlled by controller20 in combination with control devices 44A and 44B.

Input unit 92 can comprise a keyboard, a mouse, a touch panel, and thelike can be typically used. Output unit 92 can comprise a touch panel,and can additionally function as input unit 92. Recording medium 94 cancomprise any of various kinds of recording mediums such as a magnetictape, a magnetic disk, an optical disk, a magneto-optical disk, and asemiconductor memory is applicable. Output unit 96 can comprise adisplay device such as a monitor or a printer is applicable. A devicesuch as a loudspeaker that outputs sound is applicable as output unit96. In addition, control device 44B can be configured integrally withinput unit 92 and output unit 96, and a form of control device 44B isnot limited but can be a desktop type, a notebook type, a tablet type,or the like. Network 98 includes not only the Internet but also a LANand the like, and control device 44B can be connectable to anotherterminal, a database, a server, controller 20, control device 44A or thelike via network 98.

Various kinds of programs including a GTCC operation program and thelike are stored in ROM 88, and these programs are read by CPU 82 fromROM 88, loaded to, for example, RAM 86, and executed. The operationprogram can be input from recording medium 94 or network 98 via I/O port90 and stored in ROM 88. The operation program can be executed by beingread by CPU 82 from recording medium 94 or network 98 via the I/O port90 and directly loaded to RAM 86 without being stored in ROM 88. Dataand the like obtained by operations are stored in one or more memoriesout of HDD 84, ROM 88, RAM 86, and recording medium 94, and output tooutput unit 96 by operating input unit 92. In the present specification,at least one of RAM 86, ROM 88, HDD 84, recording medium 94, a storagedevice connected via the network 98, and the like will be denoted simplyas “memory,” hereinafter.

Instructions for operating supplemental firing system 18, duct burnersystem 38 and gas generator 40 can be stored in ROM 88. Suchinstructions can include commands for opening and closing shut-off valve56B when supplemental firing system 18 comes on-line or goes off-lineand commands for modulating valve 46B to control the combustion processgenerated by duct burner system 38. For example, the instructions can beconfigured to generate command signals for modulating valve 46B based oninput signals received from GT load sensor 58A, GT exhaust flow ratesensor 58B, GT exhaust temperature sensors 58C and 58D, HRSG steamtemperature sensor 58E and oxygen level sensor 58F received by I/O port90. Likewise, the instructions can be configured to generate commandsignals for modulating valve 4613 based on output of oxygen beingintroduced into duct 52 by control device 44A.

In additional examples, control device 44B can be configured to operategas generator 40, such as to ensure that an adequate supply of hydrogenhas H₂ can be supplied to duct burner system 38 for expected or forecastoperation of GTCC power plant 10. In an example, control device 44B canoperate gas generator 40 in real-time with operation of supplementalfiring system 18 to provide a live supply of hydrogen gas whilesupplemental firing system 18 is operating. In other examples, controldevice 44B can operate gas generator 40 intermittently to fill tank 42Band as duct burner system 38 draws hydrogen gas from tank 42B, such asbelow a threshold level, control device 44B can initiate operation ofgas generator 40 to fill tank 42B.

FIG. 5 is a schematic line diagram illustrating methods of generatingand combusting hydrogen fuel and oxygen in a duct burner of acombined-cycle power generation system. In an example, method 100describes a method for operating duct burner system 38 and gas generator40 of supplemental firing system 18 for heat recovery steam generator 14according the present disclosure.

At step 102, gas generator 40 can be operated to generate O₂ and H₂ gas.For example, gas generator 40 can receive instructions from one or moreof control device 44A, control device 44B and controller 20 to initiate,sustain and cease generation of O₂ and H₂ gas.

At step 104, gas generated by gas generator 40 at step 102 can beintroduced into duct burner system 38 to provide low-emission orno-emission heat to exhaust gas E.

At step 106, H₂ can be generated. In an example, gas generator 40 cancomprise an electrolyser that generates H₂ gas.

At step 107, the H₂ gas can be stored for use, either immediately orsubsequently. In an example the H₂ gas can be stored in tank 42B. Tank42B can act as an accumulator for storing of the H₂ gas when gasgenerator 40 is not operating.

At step 108, O₂ can be generated. In an example, gas generator 40 cancomprise an electrolyser that generates O₂ gas. In another example,oxygen from atmospheric or ambient air can be used as a source of O₂gas.

At step 109, the O₂ gas can be stored for use, either immediately orsubsequently. In an example the O₂ gas can be stored in tank 42A. Tank42A can act as an accumulator for storing of the O₂ gas when gasgenerator 40 is not operating.

At step 110, the H₂ gas can be pressurized. In an example, the H₂ gascan be inherently pressurized as a result of the generation process atstep 106. In examples of gas generator 40 comprising an electrolyser,the H₂ gas can be inherently pressurized. In other examples, the H₂ gasproduced at step 106 can be subsequently pressurized with anotherdevice, such as a pump or compressor. In yet other examples, pressurizedH₂ gas can be delivered in tank 42B to the site of combined-cycle powerplant 10.

At step 112, the O₂ gas can be pressurized. In an example, the O₂ gascan be inherently pressurized as a result of the generation process atstep 108. In examples of gas generator 40 comprising an electrolyser,the O₂ gas can be inherently pressurized. In other examples, the O₂ gasproduced at step 108 can be subsequently pressurized with anotherdevice, such as a pump or compressor. In yet other examples, pressurizedO₂ gas can be delivered in tank 42A to the site of combined-cycle powerplant 10.

As indicated, although steps 106, 108, 110 and 112 are indicated asseparate steps, in examples, steps 106, 108, 110 and 112 can occursimultaneously with the operation of gas generator 40.

At step 114, flow of the H₂ gas can be modulated, such as by use ofcontrol device 44B, to control the combustion process in duct 52 basedon, for example, load of gas turbine 12, flow rate of exhaust gas E,temperature of exhaust gas E and steam temperatures within HRSG 14 ascan be sensed via GT load sensor 58A, and GT exhaust flow rate sensor58B, GT exhaust temperature sensors 58C and 58D upstream and downstreamof duct burner 38, HRSG steam temperature sensor 58E and oxygen levelsensor 58F.

At step 116, flow of the O₂ gas can be modulated, such as by use ofcontrol device 44A, to control the combustion process in duct 52 basedon, for example, load of gas turbine 12, flow rate of exhaust gas E,temperature of exhaust gas E, oxygen level of exhaust gas E, and steamtemperatures within HRSG 14, as can be sensed via GT load sensor 58A,and GT exhaust flow rate sensor 58B, GT exhaust temperature sensors 58Cand 58D upstream and downstream of duct burner 38, HRSG steamtemperature sensor 58E and oxygen level sensor 58F.

At step 118, the H₂ gas can be throttled via use of an expansion devicesuch as a nozzle. Throttling of the H₂ gas can add heat to the H₂ gas tofurther increase the efficiency of steam production in HRSG 14. Forexample, expansion device 48 can be utilized to throttle the H₂ gasbefore entering duct 52, after exiting valve 46B. In other examples,throttling of the 112 gas can occur with nozzles, such as nozzle 76 ofFIG. 3.

At step 120, gas turbine 12 can be operated to produce exhaust gas E. Asdescribed, a fuel such as natural gas can be delivered to combustor 28and mixed with ambient air compressed by compressor 26. The high energygas resulting from the combustion process can be used to turn turbine,30 and heat from exhaust gas E exiting therefrom can be used in anadditional process to generate electricity with HRSG 14 and steamturbine 16.

At step 122, exhaust gas E can be directed into duct 52 of HRSG 14.

At step 124, the H₂ gas can be introduced into duct 52, such as by useof manifold 62B or manifold 72.

At step 126, the O₂ gas can be introduced into duct 52, such as by useof manifold 62A or manifold 72.

At step 128, the H₂ gas and the O₂ gas can be mixed, such as by usingmixer 50. Step 128 can be optional. Step 128 can additionally occurbefore steps 124 and 126.

Mixed or independently introduced H₂ gas and O₂ gas can be distributedwithin duct 52 via manifolds 62A, 62B or 72 to allow for an even andsustainable combustion of H₂ within duct 52. Baffle 78 can further beutilized to stabilize the combustion process by slowing the flow ofexhaust gas E at manifolds 62A, 62B or 72.

At step 130, the H₂ gas can be ignited to burn with the O₂ gas, therebyproducing heat. For example, excitor 70 can be activated by controller20 to operate ignitors 68A-68C, thereby causing a heat source topropagate combustion and flame within duct 52.

At step 132, heat from the combustion of the H₂ gas with the O₂ gas atstep 130 can be used to generate steam, such as by heating water locatedin HRSG 14. Heating of exhaust gas E with the combustion of the H₂ gascan increase the ability of HRSG 14 to turn steam turbine 16 withoutproducing harmful emissions.

The invention disclosed here enables the HRSG duct burner to efficientlycombust hydrogen by implementing a hydrogen-fueled duct burner thatutilizes oxygen as an augmenting oxidant. The implementation of theaforementioned devices, systems and methods can allow for either one ora combination of the following:

1. Improved overall thermal cycle efficiency;

2. Lower emissions; and

3. Improved duct burner operating range and the operating range andramping capabilities of the combined-cycle power plant.

Various Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventor alsocontemplates examples in which only those elements shown or describedare provided. Moreover, the present inventor also contemplates examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMS), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. A duct burner system for a combined-cyclepower plant comprising a gas turbine engine configured to generateexhaust gas and a steam generator configured to receive the exhaust gasfrom the gas turbine to heat water and generate steam, the duct burnersystem comprising: a source of hydrogen fuel; and a fuel distributionmanifold located in the steam generator to distribute the hydrogen fuelacross a length of a duct of the steam generator.
 2. The duct burnersystem of claim 1, further comprising a source of oxygen.
 3. The ductburner system of claim 2, wherein the source of hydrogen fuel comprisesa storage tank of pressurized hydrogen gas.
 4. The duct burner system ofclaim 2, wherein the source of oxygen comprises ambient air.
 5. The ductburner system of claim 2, wherein the source of hydrogen fuel and thesource of oxygen comprises an electrolysis system to generatepressurized hydrogen gas and oxygen gas.
 6. The duct burner system ofclaim 2, further comprising a burner management system to regulate flowof hydrogen fuel from the source of hydrogen fuel and oxygen from thesource of oxygen to the fuel distribution manifold based on operatingparameters of the gas turbine engine.
 7. The duct burner system of claim6, further comprising modulating valves to control flow of the hydrogenfuel and the oxygen to the fuel distribution manifold.
 8. The ductburner system of claim 1, further comprising an expansion deviceconfigured to expand hydrogen fuel before initiation of the combustionof the hydrogen fuel in the exhaust gas.
 9. The duct burner system ofclaim 8, wherein the expansion device comprises an expansion nozzlelocated between the source of hydrogen fuel and the steam generator. 10.The duct burner system of claim 8, wherein the expansion devicecomprises a nozzle located on the fuel distribution manifold.
 11. Theduct burner system of claim 1, further comprising: an igniter configuredto initiate combustion of the hydrogen fuel in the exhaust gas withinthe duct; a first electric generator configured to be driven by the gasturbine engine to generate electricity; and a steam turbine configuredto receive steam generated by the steam generator; and a second electricgenerator configured to be driven by the steam turbine to generateelectricity.
 12. A method for heating exhaust gas in a heat recoverysteam generator for use in a combined-cycle power plant, the methodcomprising: directing combustion gas of a gas turbine engine into aduct; introducing hydrogen fuel into the duct; combusting the hydrogenfuel and the combustion gas in the duct to generate heated gas; andheating water pipes in the duct with the heated gas to generate steam.13. The method of claim 12, further comprising directing oxygen into thecombustion gas.
 14. The method of claim 13, further comprising mixingthe oxygen and the hydrogen fuel in the duct before ignition.
 15. Themethod of claim 13, further comprising separately introducing the oxygenand the hydrogen fuel into the duct after ignition.
 16. The method ofclaim 13, further comprising generating the hydrogen fuel and the oxygenwith an electrolysis process.
 17. The method of claim 16, furthercomprising: pressurizing the hydrogen fuel and the oxygen; and storingthe hydrogen fuel and the oxygen in storage tanks before directing intothe duct.
 18. The method of claim 12, further comprising modulating flowof the hydrogen fuel and the oxygen to the duct based on performance ofthe gas turbine engine.
 19. The method of claim 12, further comprisingexpanding the hydrogen fuel before entering the duct.
 20. The method ofclaim 12, further comprising generating electricity with the generatedsteam.